L-tryptophan, which is an essential amino acid, has been widely used as a feed additive, a base material for medicines such as transfusion agents, etc., and a base material for health functional foods, etc. Although such L-tryptophan may be produced by chemosynthesis, enzyme reaction, fermentation methods, etc., L-tryptophan is mainly produced by direct fermentation using microorganisms at present. In early stages, the development of L-tryptophan-producing strains was carried out by mutation selection (Korean Patent Application Publication No. 1987-0001813). Along with the development of genetic engineering, the development of tryptophan-producing strains was carried out by a method for overcoming tryptophan feedback inhibition of enzymes in biosynthetic pathways via the enhancement of enzyme synthesis in metabolic processes, as in enhancing the expression of tryptophan biosynthetic enzymes. However, it is still required to develop tryptophan-producing strains having highly efficient production for industrial use.
In particular, tryptophan synthase (EC 4.2.1.20), which takes part in the final reaction stage during tryptophan biosynthesis by microorganisms, is known to use pyridoxal phosphate (PLP) as a coenzyme. Further, in the case of serine, which is used as a substrate for the tryptophan synthase reaction, phosphohydroxythreonine aminotransferase (EC 2.6.1.52) encoded by serC uses PLP as a coenzyme, and thus, PLP is considered to be an important coenzyme for tryptophan biosynthesis.
Therefore, maintaining an appropriate PLP concentration is expected to play an important role in effective reactions for the corresponding enzymes and biosynthetic reactions for the desired products. However, the coenzymes contribute to various reactions besides the tryptophan production, and therefore, a method for properly maintaining PLP level has not been discovered yet. In addition, it still remains to be elucidated whether the maintenance of PLP level in tryptophan-producing microorganisms could lead to an increase in L-tryptophan productivity.